A function whose declared type is neither void nor any (TS)

# A function whose declared type is neither void nor any (TS)

The "A function whose declared type is neither void nor any must return a value" error occurs when we explicitly set the return type of a function but the function doesn't return a value.

To solve the error, make sure to return a value from the function or remove the return type.

Here is an example of how the error occurs.

index.ts

Copied!
// ⛔️ Error: A function whose declared type is
// neither 'void' nor 'any' must return a value.ts(2355)
const getPromise = (): Promise<number> => {
  Promise.resolve(42);
};

function whose declared type is neither undefined void any

We set the return type of the getPromise function to be Promise<number> but we don't return a value from the function.

If you don't return a value from a function, the function implicitly returns undefined.

# Return a value that matches the specified type

To solve the error, return a value that matches the return type of the function.

index.ts

Copied!
const getPromise = (): Promise<number> => {
  return Promise.resolve(42);
};

return value that matches specified type

The code for this article is available on GitHub

If your function doesn't need to return anything, you can simply remove the function's return type.

index.ts

Copied!
// 👇️ const getPromise: () => void
const getPromise = () => {
  Promise.resolve(42);
};

Now the function has a return type of void, which represents the return type of functions that don't return a value.

# Dealing with complex functions with nested conditions

Sometimes you might get this error when you have a complex function with nested conditions and callbacks.

index.ts

Copied!
// ⛔️ Error: A function whose declared type is
// neither 'void' nor 'any' must return a value.ts(2355)
const getNumber = (): number => {
  function inner() {
    if (Math.random()) {
      return 100;
    }

    return 200;
  }

  inner();
};

The error occurs because we set the function's return type to be number but the function doesn't return a value.

The inner function returns a value, however, getNumber does not.

This is often a source of confusion when using callback functions. Returning a value from a nested function doesn't mean that you return the value from the outer function.

The inner() function in the example returns a number but if you want to return the number from the outer function, use an explicit return statement.

index.ts

Copied!
// ✅ OK now
const getNumber = (): number => {
  function inner() {
    if (Math.random()) {
      return 100;
    }

    return 200;
  }

  return inner();
};

use explicit return statement

The code for this article is available on GitHub

Now we explicitly return the return value of the inner function.

We had to do this because you only return a value for the function in whose scope you've used the return statement (or the implicit arrow function return).

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

I wrote a book in which I share everything I know about how to become a better, more efficient programmer.

You can use the search field on my Home Page to filter through all of my articles.

A function whose declared type is neither void nor any (TS)